Eating too much trans fat—a type of unsaturated fat known to increase the risk of developing heart disease—may be even more dangerous for women who already have heart disease, according to a new study. The finding comes from an analysis of the large women-only Nurse’s Health Study, published November 2009 in the American Heart Journal.

Trans Fat and Your Heart

Trans fats are a type of unsaturated fat that has been chemically altered to have a longer shelf life and more appealing texture for baking. However, in the past 20 years it has become apparent that this type of fat carries serious health risks. Studies have shown that consumption of trans fat doubles the risk of developing coronary artery disease in women and men by raising LDL (bad) cholesterol levels and lowering HDL (good) cholesterol levels.

While the link between coronary artery disease and trans fats is well understood, their relation to other types of heart problems, such as sudden cardiac death (SCD), is unknown. SCD occurs when the heart unexpectedly stops ( cardiac arrest) and causes death, often in people who haven’t been diagnosed with heart disease. Although any type of heart disease can cause SCD, the most common cause is a heart rhythm disturbance called a ventricular arrhythmia. It is thought that trans fat could make this type of rhythm problem more likely to occur.

New Research

The study looked at 86,762 women from the Nurse’s Health Study to see whether trans fat intake could be linked to sudden cardiac death. The women in this study filled out questionnaires about their diet and other health habits every 2 to 4 years since 1980.

Over the 26 years of the study, 317 women died of SCD. Trans fat intake was not linked to the risk of SCD in women overall. However, among women who already had some form of heart disease, those who ate the most trans fat had 3 times the risk of dying suddenly compared with women who ate the least trans fat.

These results come with one caveat: because only 100 women who already had heart disease died of SCD during the study, the researchers were not able to prove the link between trans fats and SCD was not due to chance. However, given the proven harms of trans fat, these results should be one more reason for women to limit their intake.

How to Protect Yourself

All women should avoid trans fats to reduce their risk of developing heart disease. However, the results of this study emphasize that healthy eating habits are especially important for women with heart disease. Trans fat reduction should be combined with an overall heart healthy diet to prevent your heart disease from getting worse and to reduce your risk of further problems.

There is no safe amount of trans fat, and the National Academy of Sciences recommends that you consume as little as possible while still having a balanced diet. You do not need to eliminate trans fats completely because small amounts occur naturally in the meat and milk of cows and other grazing animals. However, you should try to avoid all trans fats in processed foods. They are most commonly found in:

The FDA requires all food manufacturers to list the amount of trans fat on the Nutrition Facts label. Be sure to check the label and be aware of how much trans fat you are consuming. While you are cutting down trans fat, remember to limit your intake of other fats that can be harmful to your health: always compare food labels and choose the one that is lowest in trans fat, saturated fat, and cholesterol.